The present invention relates to a fixing device comprising, a heating roller having an elastic surface layer and incorporating a heat source therein; a press roller opposed to the heating roller so as to provide pressure against the heating roller; and a heat-resistant belt circulated while being sandwiched between the heating roller and the press roller to form a fixing nip portion, wherein a sheet medium on which an unfixed toner image is formed is passed through the fixing nip portion to fix the unfixed toner image on the sheet medium.
The present invention also relates to a fixing device comprising: a heating element having a flat surface; a press roller opposed to the flat surface so as to provide pressure against the heating element; and a heat-resistant belt circulated while being sandwiched between the flat surface and the press roller to form a fixing nip portion, wherein a sheet medium on which an unfixed toner image is formed is passed through the fixing nip portion to fix the unfixed toner image on the sheet medium.
In the former type of the fixing device, when the sheet medium is passed through the fixing nip portion to perform the fixation of the unfixed toner image, the sheet medium is curled along the outer periphery of the heating roller and becomes liable to wind around the heating roller. In order to separate the sheet medium from the heating roller, there is provided a peeler such as a peeling pawl, a peeling plate at an exit side of the fixing nip portion.
For example, Japanese Patent Publication No. 2-61030B discloses a peeler in which a plurality of flexible claws are projected from a base plate toward the exit of the fixing nip portion, so as to come in slide contact with a fixing roller, in order to separate the ejected shoot medium from the fixing roller. Japanese Utility Model Publication No. 53-117249U discloses a peeler in which a plate member is formed with slits so that divided sections are made flexible. The tip ends of the divided sections are opposed to the exit of the fixing nip portion, so as to come in slide contact with a fixing roller, in order to separate the ejected sheet medium from the fixing roller.
However, in such a configuration that the peeler comes in slide contact with the fixing roller, irrespective of the degree of the sliding pressure, the surface of the fixing roller (the heating roller and/or the press roller) is liable to be subjected to damage, wear, and deterioration. In particular, such phenomenon becomes remarkable in the recent image forming apparatus in which the operation speed is increased.
Meanwhile, immediately after the fixing operation (i.e., immediately after the ejection from the fixing nip portion), the toner image is not completely fixed on the shoot medium. When the peeler disclosed in the above publications comes in slide contact with such an unfixed toner image, sliding traces would be left on the image, or the unfixed toner would be transferred onto the peeler, thereby causing a defect on the obtained image, or the unfixed image would adhere the peeler, thereby interfering the conveyance of the sheet medium and causing the sheet jamming. In particular, such phenomenon becomes remarkable in the recent image forming apparatus in which the operation speed is increased.